Field of Invention
Aspects of this invention are related to surgical instruments, and are more particularly related to an accelerometer mounted on a surgical instrument.
Related Art
Accelerometers are widely used to measure shocks and vibrations. Fiber optic accelerometers are known and are in commercial use. In particular, fiber optic accelerometers that utilize Fiber Bragg Grating have been developed. Generally, prior Fiber Bragg Grating (FBG) accelerometers are of three types—axial FBG accelerometers, flexural FBG accelerometers, and hybrids of axial and flexural accelerometers.
FIG. 1A illustrates a first example of an axial FBG accelerometer 100. A pre-tensioned optic fiber 102 includes two FBGs 102A, 102B. A mass 101 is affixed to optic fiber 102 and positioned between FBGs 102A and 102B. The inertial reaction of mass 101 to a shock causes FBGs 102A and 102B to stretch or un-stretch in response to accelerations of the mass along the direction of optic fiber 102. FBGs 102A, 102B are located along the measurement axis of accelerometer 100, and are read differentially to provide temperature compensation.
An axial FBG accelerometer can have accelerometers positioned on one, two, or three axes. For example, FIG. 1B shows a tri-axial accelerometer 110. A mass 111 is positioned between FBGs 112A and 112B in a first pre-tensioned optic fiber extending along a z-axis. Mass 111 is positioned between FBGs 113A and 113B in a second pre-tensioned optic fiber extending along an x-axis. Mass 111 is positioned between FBGs 114A and 114B in a third pre-tensioned optic fiber extending along a y-axis. Each pair of FBGs along an axis functions in the same way as the pair of FBGs in FIG. 1A.
FIGS. 1C and 1D are illustrations of examples of flexural FBG accelerometers. In a flexural FBG accelerometer, a FBG attached to a flexural beam stretches or compresses as the flexural beam flexes in response to accelerations of the inertial mass of the flexural beam or a mass mounted on the beam exerting forces transverse to the fiber and the flexural beam.
In flexural FBG accelerometer 120, a first end of a tapered isosceles plate 123 is clamped to an external frame 122 of accelerometer 120. A second end of tapered plate 123 is affixed to a seismic mass 123. A single optic fiber 121 extends through an opening in external frame 122, and is bonded to tapered plate 123 with an epoxy resin. The portion of optic fiber 121 bonded to tapered plate includes a FBG. Thus, as seismic mass 123 moves, tapered plate 123 is flexed, which in turn causes the FBG to stretch and un-stretch.
In another example of a flexural FBG accelerometer 130 (FIG. 1D), a portion of a single multi-core fiber 131 extends from a clamp 133. Fiber 131 is affixed to clamp 133 that in turn is affixed to an end of a main sensor housing 132. Only a portion of the main sensor housing is shown in FIG. 1D. FBGs 134 are included in the cores of fiber 131 and positioned just outside collar 133. A mass 135 is attached to the unsupported end of fiber 131. Thus, the portion of fiber 131 with FBGs 134 that extends from collar 133 is a cantilever beam.
FIG. 1E is a cross-sectional illustration of cores 131A, 131B, 131C, 131D of fiber 131. Each of four cores 131A, 131B, 131C, 131D is positioned at a different vertex of a square 136. The relative stretch and compression of FBGs in opposite cores of the fiber are measured to determine the bending of fiber 131 in response to accelerations of mass 135.
The third type of accelerometer (FIG. 1F) is a hybrid of the two former types of accelerometers. Hybrid accelerometer 140 includes a mass 141 on the end of a beam 142. The combination of mass 141 and beam 142 acts via a bell crank or lever to apply an axial load to stretch or un-stretch FBG 144 in optic fiber 143 in a manner similar to the axial accelerometers described above.
The accelerometers described above are suitable for use in industrial applications. However, in a teleoperated surgical application, a FBG based accelerometer was not used. Instead, a micro-electro-mechanical system (MEMS) accelerometer was used.
FIG. 1G is an illustration of a patient side cart 150 of a teleoperated surgical system. An instrument manipulator 152 is positioned at a distal end of a setup arm 151. A sterile adapter is mounted on instrument manipulator 152 and then a surgical instrument is mounted on the sterile adapter and instrument manipulator 152 combination. A MEMS accelerometer apparatus 155 is mounted just distal of a housing 154 of surgical instrument 153 on the distal portion of a surgical instrument manipulator 152.
Thus, considering the confined space and limited volume of the distal end of the surgical instrument tube of surgical instrument 153, MEMS accelerometer apparatus 155 was mounted external to a patient and external to the surgical instrument tube of surgical instrument 153. The surgical instrument tube of surgical instrument 153 is sometimes referred to as a shaft. MEMS accelerometer apparatus 155 is positioned external to the proximal end of the surgical instrument tube of surgical instrument 153. Also, a MEMS accelerometer was used in the teleoperated surgical application instead of the FBG accelerometers that be may be used in industrial applications.